Radiation is energy that travels as a wave. Visible light, including the familiar spectrum of light7 that becomes visible in a rainbow, is an example of radiation. When an ordinary digital camera takes a picture of a tree, for example, it receives the waves of visible light that are reflected off the tree. When these waves enter the camera through the lens, theyre processed by the camera, which then puts the image together.
Waves of infrared radiation are longer than waves of visible light, so ordinary digital cameras dont see them, and neither do the eyes of human beings. Although invisible to the eye, longer infrared radiation can be detected as warmth by the skin.
Thats a key idea to why WISE will be able to see things other telescopes cant. Not everything in the universe shows up in visible light. Asteroids, for example, are giant rocks that float through space but they absorb most of the light that reaches them. They dont reflect light, so theyre difficult to see. But they do give off infrared radiation, so an infrared telescope like WISE will be able to produce images of them. During its mission WISE will take pictures of hundreds of thousands of asteroids.
Brown dwarfs8 are another kind of deep-space object that will show up in WISEs pictures. These objects are failed stars which means they are not massive enough to jump start9 the same kind of reactions that power stars such as the sun. Instead, brown dwarfs simply shrink and cool down. Theyre so dim that theyre almost impossible to see with visible light, but in the infrared spectrum they glow.
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